A hybrid powertrain or driveline may include a belt integrated starter/generator (BISG) to charge a battery of a vehicle, provide propulsion power to the vehicle, and to start an engine of the vehicle. The BISG may have a rated positive output torque (e.g., a maximum torque provided by the BISG to propel the vehicle) and a rated negative output torque (e.g., a maximum torque absorbed by the BISG from the powertrain or driveline to slow the vehicle and/or to charge an electric energy storage device). The BISG may also have a rated speed (e.g., a maximum or threshold rotational speed of the BISG that is not to be exceeded). If the BISG is matched with a large displacement engine, the BISG may not have sufficient output torque to rotate the engine at cranking speed (e.g., 250 RPM) during engine starting. Nevertheless, pulleys with a ratio other than 1:1 may be placed between the BISG and the engine to provide mechanical advantage to the BISG so that the BISG may rotate the engine at cranking speed. However, the pulley ratio may cause BISG speed to be significantly greater than engine speed such that BISG speed may exceed rated BISG speed if the engine is operated at higher speeds. Therefore, it may be desirable to provide a way of cranking an engine via a BISG without exceeding a rated speed of the BISG at higher engine speeds.
The inventors herein have recognized the above-mentioned issues and have developed a powertrain operating method, comprising: closing a BISG control clutch in response to a BISG torque not being equal to zero and BISG speed less than the threshold speed via the controller; and opening the BISG control clutch in response to the BISG torque being equal to zero or BISG speed being greater than the threshold speed via the controller.
By closing a BISG control clutch in response to a BISG torque not being equal to zero and BISG speed less than a threshold speed, it may be possible to crank the engine, provide propulsion torque to a powertrain via the BISG, and charge a battery via the BISG at BISG speeds that are less than the threshold speed (e.g., the rated speed of the BISG). Further, by opening the BISG control clutch in response to BISG output torque being equal to zero or BISG speed being greater than the threshold speed, it may be possible to operate an engine at high speeds without exceeding a rated speed of the BISG. Further, by opening the BISG control clutch when BISG output torque is zero, the BISG may freewheel without having to follow engine speed so that the possibility of BISG degradation may be reduced.
The present description may provide several advantages. In particular, the approach may allow smaller BISGs to crank large displacement engines without exceeding rated speed of the BISG. Further, the approach may reduce BISG degradation. Further still, the approach may improve vehicle operation during conditions where a BISG control clutch is degraded.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.